Configuration option to include auto purge - yes or No.
Yes means purge should happen automatically leaving last 3 Iteration.
User can also specify the number of iteration needed.
Auto Purge Iteration = 5
(This means if a part is saved 50 times, only the last 5 will be retained)
"Auto Purge Iteration = 5"
Or you could have Off/#, where off would be current functionality and # would be the number of iterations that you would like to have saved.